FIG. 1 shows a conventional twin roll continuous casting machine based on an invention disclosed in JP-8-300108A.
This twin roll continuous casting machine comprises a pair of chilled rolls 1, a pair of side weirs 2 associated with the chilled rolls 1, a pair of pinch rolls 4 for pinching a strip 3 cast by the chilled rolls 1 and feeding the same to a succeeding process such as rolling, an enclosure 5 which has lateral walls confronting widthwise edges of the strip 3 and encloses a travel path of the strip 3 from the chilled rolls 1 to the pinch rolls 4, a sledding table 6 and a plurality of table rolls 7 within the enclosure 5, sealing members 8 contiguous with an upstream portion of the enclosure 5 in the direction of travel of the strip 3 so as to abut on outer peripheries of the respective chilled rolls 1 and sealing members 9 contiguous with a downstream portion of the enclosure 5 in the direction of travel of the strip 3 so as to abut on outer peripheries of the respective pinch rolls 4.
The chilled rolls 1 are horizontally arranged in parallel with each other, a nip between the rolls being adjustable to be increased or decreased depending upon thickness of the strip 3 to be cast.
Rolling directions and velocities of the chilled rolls 1 are set such that outer peripheries of the rolls are moved from above to the nip at the same velocity.
The chilled rolls 1 are structured such that cooling water may pass through the rolls.
One of the side weirs 2 is in surface contact with one ends of the respective chilled rolls 1 and the other side weir 2 is in surface contact with the other ends of the respective chilled rolls 1; molten metal is fed to a space defined by the side weirs 2 and the rolls 1 to form a molten metal pool 10.
Formation of the pool 10 and rotation of the rolls 1 which are being cooled cause the metal to solidify on the outer peripheries of the chilled rolls 1 so that the strip 3 is delivered downward from the nip.
The pinch rolls 4 are arranged downstream of the chilled rolls 1 and adjacent to a succeeding process to which the strip 3 is to be delivered.
The sledding table 6 is adapted to take two alternative postures, one for guidance of the strip 3 from the chilled rolls 1 to the pinch rolls 4 and the other not in contact with the strip 3.
The table rolls 7 are arranged to support from below the strip 3 passing via the sledding table 6 to the pinch rolls 4.
A scrap box 11 is arranged below and connected via a sealing member 80 to the enclosure 5 so as to be positioned properly under the chilled rolls 1; the scrap box 11 is adapted to withdraw any shape-defective strip 3 produced upon startup of the casting operation.
Inert gas (nitrogen gas) G is fed to the enclosure 5 and the scrap box 11 via a conduit 12 so as to retain the interior of the enclosure 5 in non-oxidative atmosphere and prevent the hot strip 3 from being oxidized.
The sealing members 8 and 9 respectively between the enclosure 5 and the chilled rolls 1 and between the enclosure 5 and the pinch rolls 4 suppress a flow of above-mentioned inert gas G outside.
However, in the twin roll casting machine shown in FIG. 1, under the influence of the hot molten metal pool 10, the more upstream in the direction of travel of the strip 3 a position in the enclosure 5 is, the higher the atmosphere temperature in the enclosure 5 is; moreover, the chilled rolls 1 are positioned at an uppermost portion of the enclosure 5 so that, because of stack effect, the inert gas G may flow outside the enclosure 5 via between the chilled rolls 1 and the sealing members 8, and ambient air flows into the enclosure 5 via between the pinch rolls 4 and the sealing members 9 in an amount corresponding to the amount of inert gas G having flowed outside.
Therefore, the enclosure 5 must be replenished with inert gas G in an amount corresponding to that of the inert gas G flowed outside so as to prevent the strip 3 from being oxidized.
The invention was made in view of the above and has its object to provide a twin roll casting machine and an operating method thereof which can reduce an amount of inert gas to be fed for prevention of a strip from being oxidized.